1. Field of the Invention
The present invention relates to a method for treating a substrate while temporarily fixing the substrate on a support with a temporary fixing material, to a stack having the temporary fixing material, and to a semiconductor device.
2. Description of the Related Art
Substrates such as semiconductor wafers need to be temporarily fixed to supports via temporary fixing materials and so on to make sure that the substrates will not move and become displaced with respect to the supports during processing (for example, dicing, backgrinding and photofabrication) or transportation (for example, transportation between apparatuses). Such temporary fixing materials are required to allow the substrates to be separated from the supports after the completion of processing and/or transportation. Several types of adhesives proposed in the art are possibly applicable to the temporary fixation of substrates (see Patent Literatures 1 and 2).
Patent Literature 1 discloses a wafer bonding (and separating) method including providing a stack including first and second substrates bonded together via a bonding composition layer formed from a composition including a cycloolefin resin and so on dissolved or dispersed in a solvent; and subjecting the stack to a temperature enough to soften the bonding layer and thereby separating the first substrate and the second substrate from each other. This bonding layer consists of a single layer.
Patent Literature 2 discloses a method for temporarily bonding a first substrate and a second substrate, in which a stack is formed during the course of temporary bonding that includes the first substrate, the second substrate, an adhesive layer bonding respective peripheral regions of the first substrate and the second substrate, and a separation layer formed of a fill material filling a central space created by the adhesive layer.
In recent processes such as photofabrication, substrates are often exposed to a high temperature environment. For example, in a mounting step in the manufacturing of stacked chips, wafers or chips are temporarily fixed to supports, then the wafers or chips are processed (for example, subjected to throughhole formation, bump formation, rewiring, wafer thinning and wafer dicing) and the chips are stacked (for example, a plated metal is melt flowed to form an electrical connection between chips), and the chips are separated from the supports.
Such cases require temporary fixing materials which can protect substrates such as semiconductor chips and bumps from damages during processing even at high temperatures without being molten, namely, which exhibit excellent heat resistance.
The realization of such temporary fixing materials entails resins having high melting temperature. However, such resins generally show high solubility in high polarity solvents. Thus, the use of high polarity solvents as processing solvents in the processing of chips and the like restricts the choice of resins for temporary fixing materials to those exhibiting high resistance to such solvents.